The video tape editing control system of the invention fulfills a growing need in the television industry for a practical means which permits accurate and rapid editing of video tapes, so that a finished edited master tape may be assembled from the video information on one or more original tapes, or directly from a video camera. The system of the invention fulfills the aforesaid need in that it provides a rugged, low cost and accurate unit which is capable of interfacing to both the cassette and open-reel types of helical scan video tape recorders for precise tape-to-tape or camera-to-tape editing.
It is conventional practice to provide video tapes with a control track in which pulses are recorded at a preselected rate for control purposes. The editing control system of the invention, in the embodiment to be described, utilizes the pulses from the video tape control track precisely to control the operation of both the playback video tape recorder and the record video tape recorder around the selected edit frame, thereby obviating the need for complicated time codes on the tapes themselves, and for ancillary complex control equipment.
The editing control system of the invention, in the embodiment to be described, includes two manually operated joysticks which serve to control the forward and reverse movement of the video tape in the playback and record video tape recorders in the vicinity of the edit frames so as to permit exact edit frames on the tapes to be selected. The joysticks provide extremely tight control of tape speed in either direction from still frame up to, for example, three times normal tape speed.
The editing system of the invention, as will be described, uses a single cathode-ray tube monitor, which monitors both the playback and record video tape recorders, and which may be controlled to provide a repeatable preview of the individual edit frames before an actual "edit" or transfer of information to the record video tape recorder is made. Moreover, digital interlock logic is provided for foolproof operation.
Although the particular editing control system to be described herein is constructed to be interfaced, for example, with a Sony VO2850 helical scan video tape recorder, it will become evident as the description proceeds that the editing control system of the invention may be adapted to interface with a wide range of both cassette-type and open-reel type video tape recorders.
As stated above, the video tape editing control system of the invention may be used in both on-line and off-line tape-to-tape editing. On-line editing commonly denotes that edit decisions are made on the same record video tape recorder in which the finished edited tape is assembled, and there is no need to tabulate edit decisions by frame numbers of the video tape. Off-line editing generally denotes that edit decisions are performed on lower cost video tape recorders than the one used to assemble the finished edited master tape. In the latter case, the frame numbers of the video tape corresponding to each edit frame must be recorded, and these frame numbers are subsequently used when the edited master tape is assembled.
In the editing control system of the invention, as mentioned above, the video signal are fed directly from the playback video tape recorder to the record video tape recorder. It is, therefore, possible to use time base correctors, processing amplifiers, drop-out compensators, or the like, without affecting in any way the operation of the editing control system. Also, since the editing control system of the invention does not process any of the video signals themselves, the quality of the video signals is unaffected by the control system.